A tolerance ring can be used to connect together mating inner and outer components. For example, a tolerance ring may be sandwiched between a shaft that is located in a corresponding bore formed in a housing, or it may act as a force limiter to permit torque to be transmitted between the shaft and the housing. The use of a tolerance ring can accommodate minor variations in the diameter of the inner and outer components without substantially affecting their interconnection.
Typically, a tolerance ring comprises a band of resilient material, e.g. a metal such as spring steel, the ends of which are brought towards one another to form a ring. A strip of projections can extend radially from the ring either outwardly or inwardly towards the center of the ring. The projections can be formations, possibly regular formations, such as corrugations, ridges, waves or fingers. The band can include an unformed region from which the projections extend, e.g. in a radial direction.
In use, the tolerance ring can be located between the components, e.g. in the annular space between the shaft and bore in the housing, such that the projections are compressed between the inner and outer components. Each projection can act as a spring and exerts a radial force against the components, thereby providing an interference fit between them. Rotation of the inner or outer component can produce similar rotation in the other component as torque is transmitted by the ring. Likewise, linear movement of either component can produce similar linear movement in the outer component as linear force is transmitted by the ring.
If forces (rotational or linear) are applied to one or both of the inner and outer components such that the resultant force between the components is above a threshold value, the inner and outer components can move relative to one another, i.e. the tolerance ring can permit them to slip.
Although tolerance rings usually comprise a strip of resilient material that is curved to allow the easy formation of a ring, e.g. by overlapping the ends of the strip, they may also be manufactured as an annular band.
During assembly of apparatus with an interference fit between components, a tolerance ring can typically be held stationary with respect to a first (inner or outer) component whilst a second component is moved into mating engagement with the first component, thereby contacting and compressing the projections of the tolerance ring to provide the interference fit. The amount of force required to assemble the apparatus may depend on the stiffness of the projections and the degree of compression required. Likewise, the load transmitted by the tolerance ring in its final position and hence the amount of retention force provided or torque that can be transmitted may also depend on the size of the compression force and the stiffness and/or configuration of the projections.
One example of the use of a tolerance ring is in a hard disk drive (HDD) pivot mount, where the tolerance ring can provide axial retention between a rotatable pivot shaft and an arm mounted thereon. In conventional pivot mounts, the tolerance ring can provide an interference fit between the arm and a bearing mounted on the shaft.
Problems can occur during assembly of parts that use tolerance rings. As the tolerance ring requires a tight fit between its adjacent parts, there may be abrasion between the ring and various parts of the apparatus, which removes small fragments from the surface of the affected parts. These fragments are known in the art as particles. In particular, parts of the projections distal to the band of the ring may generate particles when sliding relative to part(s) of the apparatus which they contact during assembly. In certain apparatus, such as a computer hard disk drive where cleanliness is essential, production of particles is extremely undesirable, as the particles can adversely affect the function of the apparatus.